IgG4 Expression in Primary Cutaneous Marginal Zone Lymphoma: A Multicenter Study.

Background: Primary cutaneous marginal zone lymphoma (PCMZL) is the second most common B-cell lymphoma of the skin. A recent study has demonstrated a strikingly high prevalence of immunoglobulin (Ig)G4 expression in PCMZL with plasmacytic differentiation.
Objective: The objective was to investigate the incidence of IgG4 expression in PCMZL, and its correlation with clinical and immunophenotypic features.
Materials and Methods: Multicenter study that utilized immunohistochemistry and in-situ hybridization to evaluate the expression of IgG4, Ig light (κ and λ), and heavy chains (IgM, IgG), and the ratio of T (CD3+) and B (CD20+) cells in biopsy specimens from 30 patients with PCMZL and to correlate these findings with the clinical features.
Results: IgG4 expression was observed in 4 out of 30 patients (13%) with PCMZL. Patients with IgG4-positive lymphomas were 57 to 77 years of age (mean, 69) at biopsy. The lesions were solitary in 2 patients with IgG4-positive lymphomas, and were most commonly located on the trunk. Patients with IgG4-negative lymphomas experienced earlier disease onset at an average age of 53 years. The majority of the IgG4-negative cases presented with localized disease, on the trunk and upper extremities. There was no significant difference in the IgG4-positive versus negative cases for the following parameters: Ig κ or λ restriction, B-cell or T-cell predominance, and site of the lesions.
Conclusions: IgG4 expression was observed in a minority of PCMZL patients. We did not identify significant clinical or immunophenotypic differences between IgG4 positive and negative cases.